Matt Romanowski

By "pressure potentiometer" do you mean a linear sensor or string pot?

Do you find pedal position to be as accurate as long G or pressure? At the bottom of the travel, there is very little movement for large pressure changes. I would think it would be difficult to translate that movement into a pressure approximation. Plus, throw in pads warming up and their friction coefficients changing and I would think that is a tough way to log the brake traces.

Veloce Raptor

I am not sure, Matt. I do know that in a full vacuum power brake system with street ABS, at the very bottom of the travel is where ABS tends to kick in, and that amout of brake is generally not useful on track anyway with a street (as opposed to motorsport) ABS. So what I was really trying to suggest was a way to measure brake pedal travel as a way to approximate how much brake the driver is using. On a 996, ther eis generally a firm pedal and not a lot of travel overall (unless the MC is leaking), and it seems relatively linear. So some sort of potentiometer would be useful if one wants to avoid cutting fluid lines (which could possibly have unintended consequences).

Mark, IMO for a full race car you should remove the TC.

MarkM

TC is fine as long as I turn the switch off on my model there is no override so when it's off it's off for good.

How would I remove it. Can I do it electronically in the ecu?

Veloce Raptor

Yes you can remove it. I am not qualified to tell you how...but I have 2 clients who race 996's who have disabled TC and I wish I could tell you how. Could it be as simple as disconnecting the TC wiring harness into the ECU? I dunno...but they have done it.

ProCoach

Mark, I've responded via PM, but at this point, it is not worth picking a fight with your tech on this because a) as a tech, I would have reservations too, on a street car and b) I do not believe brake pressure will tell you a whole lot more than long G.

The long g is the end-result of brake pressure, caliper clamping, firewall flex, rotor cF, brake friction material mu and a whole bunch of factors all combined together. Long g is at least 90% accurate in reflecting brake pressure, if the brake system is working properly. That's my experience.

For the OP, here are the channels picked up from a Bosch MS3 for 996 GT3 Cup 2002-2005:

ECU_1
BOSCH_RPM
ECU_2
BOSCH_SPEED1
Speed1
ECU_3
BOSCH_SPEED2
Speed2
ECU_4
BOSCH_OIL_PRESS
Oil Pressure
ECU_5
BOSCH_FUEL_PRESS
Fuel Pressure
ECU_6
BOSCH_ATM_PRESS
Atmospheric Pressure
ECU_7
BOSCH_FUEL_TEMP
Fuel Temperature
ECU_8
BOSCH_OIL_TEMP
Oil_ Temperature
ECU_9
BOSCH_ENGINE_TEMP
Engine Temperature
ECU_10
BOSCH_AIR_TEMP
Air Temperature
ECU_11
BOSCH_THROTT_ANG
Throttle Angle
ECU_12
BOSCH_IGNIT_ANG
Ignition Angle
ECU_13
BOSCH_AIR_CHARGE
Engine load
ECU_14
BOSCH_INJEC_TIME1
Injection time 1
ECU_15
BOSCH_INJEC_TIME2
Injection time 2
ECU_16
BOSCH_LAMBDA1
Lambda Value 1
ECU_17
BOSCH_LAMBDA_2
Lambda Value 2
ECU_18
BOSCH_LAM_CONTR1
Lambda Controller 1
ECU_19
BOSCH_LAM_CONTR2
Lambda controller 2
ECU_20
BOSCH_FUEL_USED
Injected Fuel
ECU_22
BOSCH_GEAR
Gear Number
ECU_23
BOSCH_VBATT
Battery Voltage

ir_fuel

Can it do stuff the MXL dash add-on for the EVO 4 can't? For instance the predictive laptimes. I cannot find a decent comparison chart.

MarkM

Peter thanks for your info today and before.

VR, I'll check what it takes for the TC and get back to you. But I'm not sure about your linear comment. Late in a race I am using a lot more pedal, I noticed it at Sebring. I also know I am way over braking so that's why I am particularly interested in this sensor.

I've got coaching set up for Road Atlanta and I want to make the most of it. My coach also said he'd like the pressure, but not necessary for that weekend, so maybe he's saying I'm so bad we won't be getting to 10/10ths anyway.

To be fair to my mechanic, he is a perfectionist and has worked with some of the best teams over the last 20 years. He just doesn't like cutting into key components like the brakes or the can bus. He says he has seen too many failures or problems long term when you do it. His racers never have mechanical DNFs and that is part of the reason why I think.

Van

For brake line pressure, all you need is a little fitting that screws in between the master cylinder and one of the brake lines coming out of it. It's not exactly "cutting up the system". I actually made one (because I was in a rush on a weekend) out of an old proportioning valve housing.

Things to remember - in addition to RPM and speed:
-Throttle position, brake pressure and steering angle are to monitor the driver
-Oil pressure/temp, water temp and volts are to monitor the engine's health
-Suspension movement (shock potentiometers) are to monitor the handling of the car

If you're on a budget and/or have a system with a limited # of inputs, you have to decide which is more important for you to log.

Personally, I want to monitor the driver to improve my skills. But if you're focusing on the developing the suspension package on your car, shock pots might be more useful to you.

Veloce Raptor

These 2 statements are related

ProCoach

Can't recommend that, for the reasons you post in the thread. If the travel changes, then you can't compare data.

G's are what matter, then only if you can manipulate the raw information via math channels, does brake pressure matter.

Krokodil

Longitudinal Acceleration starts changing when you get off the gas (aero drag, etc), not when you get on the brake. Brake Pressure tells you when you get on the brake - and how hard. The time in between long accel change and brake pressure change tells you how long (and where) you were coasting.

Comparing brake pressure and throttle position (TPS data from the ECU) will also tell you how long it took you to get back to throttle after brake release. Again, providing data on how long (and where) you were coasting.

Also, if you are running dual master cylinders (which I underdstand the OP is not), brake pressure will give you an indication of F/R brake bias which can be helpful in setting up the car for max braking.

Finally, if you are running an aftermarket ABS system (which some racers do), brake switch data will likely not be available through the CAN ECU connection and therefor brake presssure is your only indicator of when you actually get on the brakes.

ProCoach

Yes, first of all it's multi color. Not only the background can be triggered but the light color and intensity can be changed for various alarms or triggers. I can set up a predictive lap time or a plus/minus, updated real-time through the GPS position on either unit, but both the MXL-Dash at $910 or the G-Dash at $414 are good deals.

ProCoach

Since the long G is a derivative of speed change versus position, it's possible to synthetically generate a reasonably accurate number from a consistent speed channel...

With an internal and properly calibrated accelerometer, I can see on AiM systems with a long G sensor, Traqmate, MoTeC, Race Technology and Race-Keeper exactly when and how quickly the throttle is shut in transition, and how much and how quickly the final product of brake pressure builds. By gating the long G using a threshold, say .2G, to indicate braking, and plotting over distance (or time, but then you can't compare events easily between two laps), it's easy for me to see the braking characteristics of the driver. For the GPS derived long G (from the Video VBOX), it's harder, but braking from those cars so equipped can be compared to others that generate .vbo files. I can easily plot the time delta or the distance delta from the cessation of an arbitrary braking force (again, say -.2g) to the application of the throttle (positive long G)

Brake pressure sensors can only properly be used for setting bias when both front and rear circuits are equipped with sensors.

It is NOT true that brake pressure channel (or even a brake pressure switch channel) is required to determine the precise position or time into the lap that effective braking (above a threshold) exists. Same with the throttle application.